1. Field of the Invention
The present invention relates generally to a cellular communication system using an Orthogonal Frequency Division Multiple Access (OFDMA) scheme (OFDMA cellular communication system), and in particular, to a method for allocating subchannels in the OFDMA cellular communication system.
2. Description of the Related Art
The next generation mobile communication system requires high-speed, high-quality data transmission in order to support various multimedia services with improved quality. Recently, a large amount of research is being performed on the OFDMA scheme, which is one of the conventional schemes satisfying the foregoing requirement.
Multiple Access schemes based on an Orthogonal Frequency Division Multiplexing (OFDM) scheme can generally be classified into two schemes. A first scheme is an OFDMA scheme in which a plurality of subchannels in one OFDM symbol are shared by a plurality users in a Broadband Wireless Access (BWA) communication system. A communication system proposed by applying the OFDMA scheme to a Fixed and Mobile Broadband Wireless Access (FBWA) communication system is an Institute of Electrical and Electronics Engineers (IEEE) 802.16d/e communication system. In the IEEE 802.16d/e communication system, 2048-point Fast Fourier Transform (FFT) is used and 1702 tones are divided into 166 pilot tones and 1536 data tones. Here, the term “tone” is identical in concept to the subcarrier, and in the following description, it should be noted that the tone has a mixed concept of the tone concept and the subcarrier concept. Further, in the IEEE 802.16d/e communication system, 1536 data tones are grouped into 32 subchannels, each having 48 data tones, and the 32 subchannels are uniquely allocated to respective users.
A second scheme is a Frequency Hopping-OFDM (FH-OFDM) scheme, which is a combination of a Frequency Hopping (FH) scheme and the OFDM scheme. Both the OFDMA scheme and the FH-OFDM scheme are intended for acquiring frequency diversity gain by uniformly dispersing data tones over the entire frequency band. However, the technologies related to the OFDMA scheme and the FH-OFDM scheme, disclosed up to now, never consider separate frequency selective adaptive modulation, except the frequency diversity. Also, an IEEE 802.16e standard never takes the frequency selective adaptive modulation into consideration.